Adhesion enhanced cement coated intermedullary nail

ABSTRACT

A medication impregnated bone cement (MIBC) coated intramedullary (IM) nail for fixation of a long bone fracture comprising an IM nail base and medication impregnated bone cement. The bone cement encapsulates at least a portion of the IM nail base and forms an interface between the adjacent surfaces of the IM nail base and the bone cement. The interface between the encapsulating bone cement and the encapsulated IM nail base being enhanced to increase the adhesion of the encapsulating bone cement to the encapsulated IM nail base. The increase in adhesion being sufficient to ensure that the encapsulating bone cement remains adhered to the encapsulated IM nail base when the medication impregnated bone cement coated intramedullary nail is removed from the long bone.

FIELD OF THE INVENTION

The present invention relates generally to intermedullary nails forfixation of long bone fractures and more specifically to medicationimpregnated bone cement (MIBC) coated intramedullary (IM) nails. Mostspecifically the present invention relates to medication impregnatedbone cement (MIBC) coated intramedullary (IM) nails having an adhesionenhanced interface between the MIBC and the IM nail base.

BACKGROUND OF THE INVENTION

Rod or nail placement in the medullary cavity for securing bonefractures is a common practice in orthopedic surgery. Use of the rod isknown to inherently produce better healing in more extreme fracturesthan other procedures in which the rod is omitted. Spanning the fracturezone, the rod imposes a rigidity to the fracture area that couldotherwise be difficult to maintain during the prolonged period ofmending. When left permanently in place, the rod reinforces the bone andreduces its susceptibility to refracture.

The interlocking intramedullary nail has been widely used in thetreatment of long bone fractures in recent years. However, patients whosuffered from infection after nailing are hard to deal with. The currentmanagement of this kind of infection consists of two main objectives,one of which is infection control, which usually is achieved by nailremoval with debridement, lavage of the medullary canal and localdelivery of antibiotics. Unfortunately, removal of the intramedullarynail causes a high risk of non-union or additional fractures,challenging surgeons to prevent such fractures with few guidelines forhow this can be done. Generally, external fixation is substituted forthe removed IM nail.

To fight the infection, antibiotic-impregnated beads have been used tofill the dead space and deliver high concentration of specificantibiotics to the infected sites simultaneously, but some defects limitthe application of antibiotic beads. Specifically, filling dead spaceincompletely, being hard to take out, and a short period of implantationtime. These beads have been replaced by antibiotic spacers, andantibiotic PMMA-coated guide rods. While these methods address theproblem of infection, all of these methods are temporary and provide nosignificant stability to the fracture, except for the antibioticPMMA-coated guide rods, which provide limited stability to axial andbending forces but no rotational stability. Essentially, none of thesemethods results in stability that is comparable to a lockedintramedullary nail, and none is likely to consistently achieve bonyunion without a subsequent procedure. For this reason, surgeons havestarted using medication impregnated bone cement (MIBC) coated IM nailsto treat an infected long bone fractures.

U.S. Pat. No. 8,609,003 to Rahul Vaidya discloses a kit and method forforming medication impregnated bone cement (MIBC) intramedullary (IM)nails. The kit for forming medication impregnated bone cement (MIBC)intramedullary (IM) nails includes a molded tube including an attachmentmeans at one end to allow for attachment of the molded tube to aconventional bone cement gun, the other end of the molded tube isadapted to allow for insertion of a IM nail thereinto. This allows forease of creation of an medication impregnated bone cement coatedintramedullary nail.

In use such an MIBC coated IM nail would be inserted into a fracturedlong bone and later removed once the bone has healed. Unfortunately,sometimes when the MIBC coated IM nail is removed from the patient, theIM nail base detaches from the MIBC coating and the coating remainswithin the IM canal. This seriously complicates the patient's healingprocess as additional procedures are required to extract the MIBC fromthe IM canal.

Thus there is needed in the art an MIBC coated IM nail with increasedadhesion of the encapsulating bone cement to the encapsulated IM nailbase.

SUMMARY OF THE INVENTION

The present invention relates to a medication impregnated bone cement(MIBC) coated intramedullary (IM) nail for fixation of a long bonefracture comprising an IM nail base and medication impregnated bonecement. The bone cement encapsulates at least a portion of the IM nailbase and forms an interface between the adjacent surfaces of the IM nailbase and the bone cement. The interface between the encapsulating bonecement and the encapsulated IM nail base being enhanced to increase theadhesion of the encapsulating bone cement to the encapsulated IM nailbase. The increase in adhesion being sufficient to ensure that theencapsulating bone cement remains adhered to the encapsulated IM nailbase when the medication impregnated bone cement coated intramedullarynail is removed from the long bone.

The enhancement to increase the adhesion of the encapsulating bonecement to the encapsulated IM nail base may be created by a physicalenhancement of the interface. The physical enhancement of the interfacemay comprise indentations on the surface of the IM nail base adjacent tothe bone cement, the bone cement filling the indentations in the surfaceof the IM nail base. Alternatively, the physical enhancement of theinterface may comprise protrusions projecting from the surface of the IMnail base adjacent to the bone cement, the protrusions projecting intothe bone cement. Further, the physical enhancement of the interface maycomprise both indentations on the surface of the IM nail base adjacentto the bone cement and protrusions projecting from the surface of the IMnail base. Alternatively, the physical enhancement of the interface maycomprise an increased surface roughness of the IM nail base.

The enhancement to increase the adhesion of the encapsulating bonecement to the encapsulated IM nail base may alternatively be created bya chemical enhancement of the interface. The chemical enhancement of theinterface may comprise formation of a chemical bond between the bonecement and the IM nail base. The formation of a chemical bond betweenthe bone cement and the IM nail base may comprise deposition of anadhesive layer on the surface of the IM nail base to which the bonecement bonds. The adhesive layer may comprise a curing agent for thebone cement or a one part bio-compatible epoxy.

The formation of a chemical bond between the bone cement and the IM nailbase may alternatively comprise an interface layer between the bonecement and the IM nail base, the interface layer being deposited on theIM nail base, the interface layer bonding more strongly with both of thebone cement and the material of the IM nail base than the bone cementbonds with the material of the IM nail base. The interface layer maycomprise a layer of consisting of titanium dioxide (TiO₂) or aluminumoxide (Al₂O₃) deposited on the surface of the IM nail base. Theinterface layer may alternatively comprise a thin-film PMMA or CPCprecoating deposited on the surface of the IM nail base to which thebone cement cross-links as it polymerizes.

The formation of a chemical bond between the bone cement and the IM nailbase may also comprise a direct chemical bond between the bone cementand the surface of the IM nail base. The IM nail base may comprise apolymer which cross-links or copolymerizes with the bone cement as itpolymerizes.

The IM nail base may comprise one or more bio-compatible materialsselected from the group consisting of: metals, polymers, reinforcedpolymers, polymers with radiopaque additives and composite metal/polymermaterials and combinations thereof. The IM nail base may comprise a PMMAor CPC polymer with embedded carbon fibers and a radiopaque contrastagent. The radiopaque contrast agent may comprise zirconium dioxide(ZrO₂) or barium sulphate (BaSO₄). The MIBC may be impregnated with oneor more medications selected from the group consisting of antibiotics,antifungals, antineoplastics, and recombinant human bone morphogeneticprotein.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a typical prior art MIBC coated IM nail with hardenedMIBC formed about the IM nail base;

FIG. 2 depicts the prior art interface between the hardened MIBC and theIM nail base;

FIG. 3A depicts the interface between the hardened MIBC and the IM nailbase and further shows indentations in the surface of the IM nail base;

FIG. 3B depicts a plate type IM nail base 2 having indentations thatextend completely therethrough;

FIG. 4 depicts the interface between the hardened MIBC and the IM nailbase and further shows protrusions from the surface of the IM nail base;

FIG. 5 depicts the enhanced interface between the hardened MIBC and theIM nail base which is caused by an increase in the surface roughness ofthe IM nail base; and

FIG. 6 depicts the chemically enhanced interface between the hardenedMIBC and the IM nail base.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to improved medication impregnated bonecement (MIBC) coated intramedullary (IM) nails. One type of well knownbone cement is Polymethyl-methacrylate (PMMA), PMMA is widely used forimplant fixation in various Orthopaedic and trauma surgery. In reality,“cement” is a misnomer because the word cement is used to describe asubstance that bonds two things together. However, PMMA acts as aspace-filler that creates a tight space which holds the implant againstthe bone and thus acts as a grout. Bone cements have no intrinsicadhesive properties, but they rely instead on close mechanical interlockbetween the irregular bone surface and the prosthesis.

As detailed in U.S. Pat. No. 8,609,003 issued to Rahul Vaidya (thedisclosure of which is hereby incorporated by reference), a medicationimpregnated bone cement (MIBC) coated intramedullary (IM) nail iscreated by insertion of a base IM nail into a mold and pumping apremixed liquid of medication impregnated bone cement into the mold. Onetype of bone cement, known as PMMA bone cement, is an acrylic polymerthat is formed by mixing two sterile components: a liquid MMA monomerand a powered MMA-styrene co-polymer. When the two components are mixed,the liquid monomer polymerizes around the pre polymerized powderparticles to form hardened PMMA. Bone cement has proven particularlyuseful because active substances, can be added to the powder component.This makes bone cement a modern drug delivery system that delivers therequired drugs directly to the surgical site. Various antibiotics havebeen successfully mixed and used with bone cements like Gentamycin,Tobramycin, Erythromycin, Cefuroxime, Vancomycin, Colistin etc. Thebasic requirement, being that the mixable antibiotic should be heatresistant and should last for a relatively long duration of time.

Other types of medications useful in the MIBC of the present inventionare antifungal drugs (eg. fluconazole and amphotericin B),antineoplastics (e.g. andriamycin and cisplatin), and recombinant humanbone morphogenetic protein,

Other types of bone cement may also be used to coat the IM nail base.One such material are the calcium phosphate bone cements. Calciumphosphate cements (CPCs) are self-setting bioactive materials withunique properties for bone regeneration applications. CPCs can be usedfor the replacement of damaged bone. They are cementing systemsconsisting of powder and liquid phases. The mixing odf the phases causesa chemical reaction accompanied by setting and then hardening. CPCscombine features such as osteo-conductivity, the ability to maintainvital functions of osteogenic cells, biocompatibility, the lack ofnegative reactions from the body, and its fomability By controlling thephase composition it becomes possible to regulate the rate ofbiodegradation (dissolving in the body) of CPCs, allowing for theapplicability of the material in bone tissue regeneration, so calledtissue engineering. CPCs are without the drawbacks of polymer cementsbased on polymethyl-methacrylate caused by toxic degradation products.The weakly exothermic polymerization reactions of CPCs and their lowshrinkage upon setting are very positive qualities of these cements. CPCcements can be durable and dense or porous. Their porosity is animportant factor in their ability to deliver osteogenic cells andimpregnated medications.

When medication impregnated bone cement sets/hardens it forms anencapsulating coating around the IM nail base. FIG. 1 depicts a typical(prior art) MIBC coated IM nail 1 with hardened MIBC 3 formed about thebase IM nail 2 and including holes 7 to accommodate fastening means suchas locking screws. FIG. 2 depicts the prior art interface 4 between thehardened MIBC 3 and the base IM nail 2. This interface 4 is generallysmooth and this smoothness can provide inadequate adhesion between thebase IM nail 2 and the MIBC 3. This can be especially true when the MIBCcoated IM nail 1 is removed from the patient's bone after union andhealing have occurred. If the MIBC separates from the base IM nail itmay remain in the patient's IM canal, requiring additional surgicaltechniques to remove it. The can complicate and lengthen the healingprocess for the patient.

It is to this end that the present inventor has devised the improvedMIBC coated IM nail of the instant invention. The present invention isan improved bone cement coated IM nail for fixation of a long bonefractures and includes an IM nail base 2 and bone cement 3 whichencapsulates at least a portion of the IM nail base. Further, theinterface between the encapsulating bone cement 3 and the encapsulatedIM nail base 2 is enhanced to increase the adhesion of the encapsulatingbone cement 3 to the encapsulated IM nail base 2, such that the increasein adhesion is sufficient to ensure that the encapsulating bone cement 3remains adhered to the encapsulated IM nail base 2 when the cementcoated IM nail is removed from the long bone.

The increase in the adhesion strength between the bone cement and thebase IM nail may be the result of physical enhancement of the IM nailbase surface. Such a physical enhancement may come from creation ofindentations in the surface of the base im nail. FIG. 3A depicts theinterface 4 between the hardened MIBC 3 and the base IM nail 2 andfurther shows indentations 5 in the surface of the base IM nail 2. Theindentations 5 increase the surface area of the interface 4 between theMIBC 3 and the base IM nail 2. The indentations 5 also allow forinterpenetration of the MIBC 3 into the base IM nail 2, which in turnallows for increased adhesion as the coated im nail is removed from thepatient's long bone. The indentations 5 may be deep or shallow as neededand may be angled into the base nail so as to increase the adhesion withrespect to forces acting on the interface during the removal of thecoated nail. It should also be noted that the indentations 5 maytraverse the entire depth of the IM nail base such that the MIBCinfiltrates all the way through the IM nail base. The indentations 5 maybe placed and spaced evenly on the base IM nail surface or may berandomly spaced and placed. The indentations 5 may also beplaced/distributed in a such a way as to enhance the adhesion incritical areas of the interface as needed or desirable. The indentations5 may be uniform in size and shape across the surface of the base IMnail or may be different shapes and sizes as needed, or even randomshapes and sizes.

FIG. 3B depicts a plate type IM nail base 2 having indentations 5 in thesurface there which may extend completely therethrough. The IM nail base2 also includes holes 7 to accommodate fastening means such as lockingscrews. As noted above when the indentations 5 extend completely throughthe entire depth of the IM nail base 2, the MIBC infiltrates all the waythrough the IM nail base 2, thereby allowing for enhanced adhesion ofthe MIBC to the IM nail base.

Another physical enhancement of the surface of the base IM nail may comefrom creation of protrusions from the surface of the base im nail. FIG.4 depicts the interface 4 between the hardened MIBC 3 and the base IMnail 2 and further shows protrusions 6 from the surface of the base IMnail 2. The protrusions 6 increase the surface area of the interface 4between the MIBC 3 and the base IM nail 2. The protrusions 6 also allowfor interpenetration of the base IM nail 2 into the MIBC 3, which inturn allows for increased adhesion as the coated im nail is removed fromthe patient's long bone. The protrusions 6 long or short as needed andmay be angled from the base nail so as to increase the adhesion withrespect to forces acting on the interface during the removal of thecoated nail. The protrusions 6 may be placed and spaced evenly on thebase IM nail surface or may be randomly spaced and placed. Theprotrusions 6 may also be placed/distributed in a such a way as toenhance the adhesion in critical areas of the interface as needed ordesirable. The protrusions 6 may be uniform in size and shape across thesurface of the base IM nail or may be different shapes and sizes asneeded, or even random shapes and sizes.

It should be noted that a combination of both indentations 5 andprotrusions 6 may also be used if desirable to further enhance theadhesion of the encapsulating bone cement 3 to the encapsulated IM nailbase 2. This combination of both indentations 5 and protrusions 6 is amacroscopic version of yet another physical enhancement of the surfaceof the base IM nail. This third example of physical enhancement of thesurface of the base IM nail is an increase in the surface roughness ofthe surface of the base im nail. This increase in surface roughness canbe thought of as a microscopic combination of both indentations 5 andprotrusions 6 on the surface of the base IM nail. FIG. 5 depicts theenhanced interface 4′ between the hardened MIBC 3 and the base IM nail 2which is caused by an increase in the surface roughness of the base IMnail.

Another method of enhancing the adhesion between the encapsulating bonecement 3 and the encapsulated IM nail base 2 is by chemical enhancement.That is, by chemical enhancement of the bond between the IM nail baseand the bone cement. FIG. 6 depicts the chemically enhanced interface 4″between the hardened MIBC 3 and the base IM nail 2. The chemicallyenhance interface 4″ may include an adhesive layer on the base IM nail,an interface layer (placed between the bone cement and IM nail base)which bonds more strongly to each of the bone cement and the IM nailbase than does the bone cement directly to the nail base, and a directchemical bond between the bone cement and the IM nail base.

The adhesive layer is deposited on the IM nail base and may be anyadhesive that is bio-compatible and bonds to both bone cement and thematerial of the IM nail base. Some examples of such an adhesive are acuring agent for the bone cement and a one part bio-compatible epoxy.The interface layer between the bone cement and the IM nail base isdeposited on the IM nail base and bond more strongly with both of thebone cement and the material of the IM nail base than the bone cementbonds with the material of the IM nail base. The interface layer may actas a primer allowing the bone cement to adhere more strongly to the baseIM nail. Such a primer layer may be a layer of titanium dioxide (TiO₂)or aluminum oxide (Al₂O₃). The primer may also be a thin-film PMMAprecoating of the IM nail base to which the bone cement may cross-linkas it polymerizes. Finally, the bone cement may be directly chemicallybonded with the base IM nail. This can be accomplished by creation of abase IM nail formed from a polymer which reacts (cross-links orcopolymerizes) with the bone cement as it polymerizes.

The base IM nail may be formed from bio-compatible metals, polymers,reinforced polymers, polymers with radio-opaque additives and compositemetal/polymer materials and combinations thereof. One useful base IMnail may be a PMMA polymer with embedded carbon fibers and a radiopaquecontrast agent. Commercially available cements use either zirconiumdioxide (ZrO₂) or barium sulphate (BaSO₄) as the radiopaque contrastagent. Zirconium dioxide is one hundred times less soluble than bariumsulphate and has less effect on the mechanical properties of the cement.

As described in U.S. Pat. No. 8,609,003 patent, instead of the basemetal IM nail, the cement nail can be formed on other base/supportelements. For example, the base may be a metal strip or plate with holesthrough the strip in the proper locations to allow for spacers to createlocking screw holes in the molded cement nail. In addition to thelocking screw holes, the strip or plate may include indentations thatextent all the way through the strip or plate allowing MIBC toinfiltrate completely therethrough. This same concept of indentationsextending through the IM nail base can be applied to convention Anotheralternative may be metal wires, such as straight or curved wires, coils,flat mesh, or mesh cages. The metal wires act like reinforcing steel barin concrete structural constructions. This wire structure is usefulbecause the cement nail alone (without the support) is strong incompression, but is weak in tension. Thus the base provides addedtension strength to the cement nail. While metal wire is describedabove, other materials may be used to form the support as long as itadds to the strength of the cement nail. If the base support is notadapted to be attached to an IM nail insertion handle, a proximal endstub of a conventional IM nail may be formed into the cement nail.

It is to be understood that the disclosure set forth herein is presentedin the form of detailed embodiments described for the purpose of makinga full and complete disclosure of the present invention, and that suchdetails are not to be interpreted as limiting the true scope of thisinvention as set forth and defined in the appended claims.

I claim:
 1. A medication impregnated bone cement (MIBC) coatedintramedullary (IM) nail for fixation of a long bone fracturecomprising: an IM nail base; and medication impregnated bone cement;wherein said bone cement encapsulates at least a portion of said IM nailbase and forms an interface between the adjacent surfaces of said IMnail base and said bone cement; said interface between saidencapsulating bone cement and said encapsulated IM nail base beingenhanced to increase the adhesion of said encapsulating bone cement tosaid encapsulated IM nail base; wherein said increase in adhesion issufficient to ensure that said encapsulating bone cement remains adheredto said encapsulated IM nail base when said medication impregnated bonecement coated intramedullary nail is removed from said long bone.
 2. TheMIBC coated IM nail of claim 1, wherein said enhancement to increase theadhesion of said encapsulating bone cement to said encapsulated IM nailbase is created by a physical enhancement of said interface.
 3. The MIBCcoated IM nail of claim 2, wherein said physical enhancement of saidinterface comprises indentations on said surface of said IM nail baseadjacent to said bone cement, said bone cement filling said indentationsin said surface of said IM nail base.
 4. The MIBC coated IM nail ofclaim 2, wherein said physical enhancement of said interface comprisesprotrusions projecting from said surface of said IM nail base adjacentto said bone cement, said protrusions projecting into said bone cement.5. The MIBC coated IM nail of claim 2, wherein said physical enhancementof said interface comprises both: a) indentations on said surface ofsaid IM nail base adjacent to said bone cement, said bone cement fillingsaid indentations in said surface of said IM nail base; and b)protrusions projecting from said surface of said IM nail base adjacentto said bone cement, said protrusions projecting into said bone cement.6. The MIBC coated IM nail of claim 2, wherein said physical enhancementof said interface comprises an increased surface roughness of said IMnail base.
 7. The MIBC coated IM nail of claim 1, wherein saidenhancement to increase the adhesion of said encapsulating bone cementto said encapsulated IM nail base is created by a chemical enhancementof said interface.
 8. The MIBC coated IM nail of claim 7, wherein saidchemical enhancement of said interface comprises formation of a chemicalbond between said bone cement and said IM nail base.
 9. The MIBC coatedIM nail of claim 8, wherein said formation of a chemical bond betweensaid bone cement and said IM nail base comprises deposition of anadhesive layer on said surface of said IM nail base to which said bonecement bonds.
 10. The MIBC coated IM nail of claim 9, wherein saidadhesive layer comprises a curing agent for said bone cement.
 11. TheMIBC coated IM nail of claim 9, wherein said adhesive layer comprises aone part bio-compatible epoxy.
 12. The MIBC coated IM nail of claim 8,wherein said formation of a chemical bond between said bone cement andsaid IM nail base comprises an interface layer between said bone cementand said IM nail base, said interface layer being deposited on the IMnail base, said interface layer bonding more strongly with both of saidbone cement and the material of said IM nail base than said bone cementbonds with said material of said IM nail base.
 13. The MIBC coated IMnail of claim 12, wherein said interface layer comprises a layer ofconsisting of titanium dioxide (TiO₂) or aluminum oxide (Al₂O₃)deposited on said surface of said IM nail base.
 14. The MIBC coated IMnail of claim 12, wherein said interface layer comprises a thin-filmPMMA or CPC precoating deposited on said surface of said IM nail base towhich said bone cement cross-links as it polymerizes.
 15. The MIBCcoated IM nail of claim 8, wherein said formation of a chemical bondbetween said bone cement and said IM nail base comprises a directchemical bond between said bone cement and said surface of said IM nailbase.
 16. The MIBC coated IM nail of claim 15, wherein said IM nail basecomprises a polymer which cross-links or copolymerizes with said bonecement as it polymerizes.
 17. The MIBC coated IM nail of claim 1,wherein said IM nail base comprises one or more bio-compatible materialsselected from the group consisting of: metals, polymers, reinforcedpolymers, polymers with radiopaque additives and composite metal/polymermaterials and combinations thereof.
 18. The MIBC coated IM nail of claim17, wherein said IM nail base comprises PMMA or CPC polymer withembedded carbon fibers and a radiopaque contrast agent.
 19. The MIBCcoated IM nail of claim 18, radiopaque contrast agent compriseszirconium dioxide (ZrO₂) or barium sulphate (BaSO₄).
 20. The MIBC coatedIM nail of claim 1, wherein said MIBC is impregnated with one or moremedications selected from the group consisting of antibiotics,antifungals, antineoplastics, and recombinant human bone morphogeneticprotein.